The commercial viability of allograft tissues is in part a function of the physical appearance, the biocompatibility, and the mechanical properties of the tissue. Individuals responsible for the decision to use or not use a given allograft often evaluate the aesthetics of the product in reaching a decision. For example, ligament allograft material that is “yellow” is often rejected by the surgeon for implantation in favor of an allograft that is not discolored. Likewise for soft tissue, in particular, dermis and cardiovascular tissue, color and appearance are deciding factors used by most surgeons in the operating room.
Tissue banks responsible for the processing of allografts employ many different cleaning, rinsing, soaking, and washing steps in an effort to produce a product that is safe, viable for implantation, and commercially desirable. While many of the steps used meet these goals, they often fall short of effectively producing a commercially desirable and functional product. This shortcoming can stem from inadequacy of the existing process to clean the product or it may stem from damage caused by the cleaning treatment that negatively impacts the biological and biomechanical properties of the allograft.
Additionally, the numerous steps required to achieve an acceptable product for distribution add to the cost of the final graft. These steps require extra processing time and personnel, and can often vary in effectiveness. Ideally a process for preparing allografts would include a step that could preserve the essential properties of the allograft, remove the antigenic matter and any discoloration from the allograft, take a minimum amount of processing time, prepare the allograft for sterilization and increase the commercial desirability by positively impacting the aesthetics of the product.
Generally, soft tissue grafts are manually cleaned to purify them of all materials that adversely affect their implantation. Currently, most prior art techniques are found to impair both the biomechanical properties and inductive properties of the soft tissue. The prior techniques used for extraction of impurities disrupt the collagen network of the soft tissue by cross-linking or degradation, further affecting the mechanical properties of the soft tissue graft. Since, the implanting of soft tissue grafts is generally carried out for the purpose of repairing damaged soft tissue or replacing an impaired soft tissue, it is desirable to eliminate the problem of recolonization because of reduced or minimal blood flow, which is essential. It would therefore be advantageous to have available soft tissue grafts with biomechanical properties that are almost equivalent to those of natural soft tissue.
There are inherent risks involved with allografts since soft tissue is being taken from a donor generally with an unknown medical history. For example, an infectious disease from the donor could be passed on to the recipient. Apart from the risks of infection, the main complications related to the use of allografts are rejection, inflammatory response from residual foreign material in the transplanted graft and, when appropriate, the unsuccessful recolonization of the implanted soft tissue. The unsuccessful recolonization of the grafts today poses a particularly significant problem.
To mitigate these risks, various attempts aiming to reduce or eliminate these complications have been made. These procedures are generally based on the principle of extracting the blood or blood constituents and lipids from the soft tissue before implantation. Such residual blood or blood constituents and lipids contained in the soft tissue are the cause of significant rejection reactions. These rejection reactions are also related to the presence of contaminants such as endotoxins in the tissue.
The use of organic solvents to extract blood, blood constituents and lipids from soft tissue is known. The most commonly used solvents are ethylene diamine, hydrogen peroxide, ethanol, acetone and various chlorinated solvents such as chloroform or dichloromethane. However, the solvents used for protein extraction are often highly toxic. Because of this toxicity, the soft tissues must be carefully rinsed, which often proves to be difficult, given their density and delicate structure (collagenous network).
In accordance with the need for proper preparation of donor soft tissue, gentle and reliable sterilization methods are needed that result in greater than 106 log reductions of microbial contaminants without impacting the properties of the donor soft tissue being sterilized.
A need has developed for sterilization of biological tissues, including macromolecular biopolymers, due to the common practice of tissue implantation. However, most sterilization techniques for soft tissue have been found to be incompatible with the tissue. Steam and gamma radiation result in a significant decrease in tissue integrity and soft tissue strength due to cross-linking. Cross-linking disrupts the collagenous network, increasing the stiffness of the collagen fibers and decreasing the mobility of the graft. Certain antibacterial washes have been used to disinfect tissue, but incomplete sterilization is achieved and the washes leave residual toxic contaminants in the tissues. Ethylene oxide also reacts with biological tissue and is thus an undesirable sterilant for such reason.
Recently, in U.S. Pat. No. 7,108,832, incorporated herein by reference and commonly owned by assignee of this application, a highly effective sterilization process is disclosed.
It therefore would be highly desirable to provide a process for cleaning soft tissue prior to the tissue being sterilized.